String theory - the basic idea
Have you read the preceding page on "The search for a new theory combining general relativity and quantum mechanics"?
String theory postulates that every particle is composed of a tiny filament of energy, some hundred billion billion times smaller than a single atomic nucleus, shaped like a little string. According to string theory, the mass of an elementary particle is determined by the energy of the vibrational pattern of its internal string. Heavier particles have internal strings that vibrate more energetically while lighter particles have internal strings that vibrate less energetically. Since the mass of a particle determines its gravitational properties, there is a direct association between the pattern of string vibration and a particle’s response to the gravitational force.
According to string theory, the observed properties of each elementary particle arise because its internal string undergoes a particular resonant vibrational pattern, and what appear to be elementary particles are actually tiny pieces of vibrating string.[1] A tiny string vibrating in one pattern would have the mass and electric charge of an electron. A tiny string vibrating in a different pattern would have the requisite properties to identify it as a quark, or a neutrino or another particle. String theory harmonises general relativity and quantum mechanics, and provides a truly unified theory, since all matter and all forces, gravity included, are proposed to arise from one basic ingredient: oscillating strings.
As we have seen, the microscopic realm is characterised by constant jittering, “a roiling frenzy awash in a violent sea of quantum fluctuations”. String theory softens these violent quantum fluctuations by “smearing out” the short distance properties of time and space. To gain an intuitive feel for what is involved here, the surface of the polished table in front of you may appear perfectly smooth, but at a microscopic level, the surface is discrete, grainy and bumpy, and our stumpy, extended fingers “smear out” the microscopic discreteness. Similarly, string theory is unable to probe sub-Planck scale distances, and although the resonant fluctuations are still substantial, this “smearing” smooths them out just enough to cure the incompatibility between General Relativity and Quantum Mechanics. In other words, in string theory there is a limit to how finely one can probe the universe, and the Planck scale draws the line in the sand.[2]
[1] Greene (2000), 145-146; Greene (2005), 17-18.
[2] Greene (2000), 152, 152-157.
According to string theory, the observed properties of each elementary particle arise because its internal string undergoes a particular resonant vibrational pattern, and what appear to be elementary particles are actually tiny pieces of vibrating string.[1] A tiny string vibrating in one pattern would have the mass and electric charge of an electron. A tiny string vibrating in a different pattern would have the requisite properties to identify it as a quark, or a neutrino or another particle. String theory harmonises general relativity and quantum mechanics, and provides a truly unified theory, since all matter and all forces, gravity included, are proposed to arise from one basic ingredient: oscillating strings.
As we have seen, the microscopic realm is characterised by constant jittering, “a roiling frenzy awash in a violent sea of quantum fluctuations”. String theory softens these violent quantum fluctuations by “smearing out” the short distance properties of time and space. To gain an intuitive feel for what is involved here, the surface of the polished table in front of you may appear perfectly smooth, but at a microscopic level, the surface is discrete, grainy and bumpy, and our stumpy, extended fingers “smear out” the microscopic discreteness. Similarly, string theory is unable to probe sub-Planck scale distances, and although the resonant fluctuations are still substantial, this “smearing” smooths them out just enough to cure the incompatibility between General Relativity and Quantum Mechanics. In other words, in string theory there is a limit to how finely one can probe the universe, and the Planck scale draws the line in the sand.[2]
[1] Greene (2000), 145-146; Greene (2005), 17-18.
[2] Greene (2000), 152, 152-157.